There is known a pulse wave detecting apparatus which detects a pulse wave using a pulse wave sensor which is pressed against an arterial vessel of a living body via a body surface with an optimum pressing force, the optimum pressing force being determined based upon a pulse wave detected by the pulse wave sensor while the pressing force applied to the pulse wave sensor is changed over a predetermined range.
In this pulse wave detecting apparatus, the pulse wave sensor is pressed against a wrist, for example. An optimum range of the pressing force applied to the pulse wave sensor within which a pulse wave having an appropriate magnitude is detected, is of considerably small width, in the case where the arterial vessel is positioned at a position nearer to the surface of the wrist than to the radius bone and tendon and for this reason the arterial vessel substantially is flattened before the pulse wave sensor is pressed toward the radius bone and tendon with a considerably great force, where the subject is so fat that the arterial vessel is positioned at a considerably deep position from the surface of the wrist, or where the arterial vessel is considerably thin. If this optimum pressing force range is considerably narrow, even a slight change in the pulse wave sensor pressing force, caused during the pulse wave detection, will lead to difficulty in detecting a pulse wave having an appropriate magnitude. This insufficient stability of detection of the pulse wave is due to the subject himself, not an error caused in the pulse wave detecting apparatus. For this reason, sufficient stability of detection of pulse wave cannot be obtained by re-activating the pulse wave detecting apparatus. In these cases, therefore, it is required to promptly identify that the stability of detection of pulse wave is insufficient due to the subject himself and take an appropriate measure on the subject, for example moving the hand inward about the wrist.
The present invention has been developed in the above-indicated situation. It is therefore an object of the present invention to provide a pulse wave detecting apparatus capable of identifying that stability of detection of pulse wave is insufficient due to a living body itself.